The 19th-century veterinarian who nearly cracked one of medicine’s oldest mysteries

The 19th-century veterinarian who nearly cracked one of medicine’s oldest mysteries View our Twitter (X) feedView our Youtube channelView our Instagram feedView our Substack feedView our Spotify feed The 19th-century veterinarian who nearly cracked one of medicine’s oldest mysteries The Great Epizootic of 1872 gave James Law the evidence he needed to challenge centuries of thinking surrounding the origins of disease. History and SocietyScientific MethodEpidemiologyHistory Of ScienceInfectious Disease Adapted from Nary a Horse Left Standing: How a Nineteenth-Century Epidemic Transformed Medicine, Animal Welfare, and the Modern City by Lee Alan Dugatkin. As far as presenting the case for germ theory, James Law’s 45-page report “Influenza in Horses,” which appeared in the _Report of the Commissioner of Agriculture for the Year 1872_ was a tour de force of the medical geography of the Great Epizootic.

It contained detailed information on the “atmospheric conditions” that miasmists turned to over and over again, as well as a synopsis of the results of a study Law had commissioned from a microscopist colleague. It was from that combination of medical geography, meteorological data, and microscopy from which Law drew many of his conclusions. [Editor’s Note: Miasma theory is the now-debunked belief that vapors found in “bad air” caused diseases. During the second half of the 19th century, it competed with germ theory as the best explanation for illnesses and epidemics.] Law begins his report with a lengthy history of epidemics in humans and epizootics in animals from the time of the ancient Greeks onward, followed by a medical geography of the Great Epizootic.

Next, he spends page after page describing the symptoms of horse flu. In total, these three sections make up a third — 15 pages — of the report. But it’s in the next section of the report, subtitled “Causes of the Influenza,” which itself runs 24 pages, where Law is in full form on the question of whether miasma or germ theory explains the Great Epizootic.

The “Causes of the Influenza” section opens with “the old doctrine of an epidemic constitution of the atmosphere has of late years been gradually waning,” which may have been true in Law’s circle of colleagues, but was not reflective of the wide-scale acceptance of miasma theory by respected veterinarians and physicians in so many locations that were hit by the Great Epizootic. Law recognizes this reality to some extent, acknowledging that “more than any other epidemic malady, perhaps, has influenza retained its claim on an atmospheric causation.” What’s more, he makes clear, those claims assuredly were being applied to equine influenza, and in particular, that associated with the Great Epizootic. But “the epizootic of 1872 affords but the slenderest appearance of support to any of these [miasmic] hypotheses,” Law begins his argument against such claims, continuing “neither soil nor elevation has materially affected it.

The prevalence and mortality have been almost the same in the mountains of Vermont and New Hampshire as in the flat, malarious sea-coast of New Jersey, Maryland, and Virginia.” Law next turns to temperature, knowing that miasmists often argue that warmer temperatures create the “atmospheric disturbances” that cause disease. One table that Law presents shows temperature, wind velocity, and barometric pressure, as well as the amount of rain and snow that fell every day of October 1872: Indeed, the table shows each of those measurements gathered three times each day (6:00 a.m., 2:00 p.m., and 10:00 p.m.). As a comparison, Law provides another table with corresponding data for every October from 1844 to 1872.

Law was also very clear about what he was not saying. He understood that once a horse was infected, cold weather acting on an already compromised immune system could cause symptoms to be even worse, noting that “nasal and bronchial catarrhs often prevail extensively among horses, as among men, in connection with sudden and extreme variations of temperature, and especially in spring and autumn.” But cold weather was not the cause of the infection. Another miasmic bugaboo was fog, and Law tackles that in the same manner as he did other putative meteorological causes for the Great Epizootic: by employing data.